1. Field of the Invention
The present invention relates to a picture image forming apparatus for forming a composite panoramic picture image from a plurality of still digital picture images.
2. Description of the Related Art
There are known methods for jointing a pair of digital picture images including images of a same object and having overlap regions where the plurality of digital picture images overlap each other, to form a panoramic picture image or a highly fine (high resolution) picture image, for example, a method disclosed in Japanese Unexamined Patent Publication JP-A 3-182976(1991), in which two characteristic particles which are granular portions having high concentration in picture image, are sampled in each of a pair of picture images having overlap regions and the picture images are jointed together with a line connecting these as a joint line, and a method disclosed in Japanese Unexamined Patent Publication JP-A 5-122606(1993), in which the pair of picture images are jointed together at a region minimizing a difference in concentration.
There is disclosed a method described in "Picture Image Analysis Handbook", page 466, issued by Tokyo University Publication Association where in jointing a pair of picture images, the picture images are not jointed by a line such as a joint line but color tone is smoothed such that a change in concentrations of the two picture images does not become discontinuous at surroundings of the joint line.
A camera is supposed to provide a picture image describing a view in a imaging range by one imaging operation. In imaging a digital picture image by using the camera, there are a case where pan-imaging by hand holding is carried out, a case where pan-imaging is carried out by using a tripod, a case where imaging is performed by installing a plurality of cameras having overlapped imaging ranges.
Pan-imaging indicates plural times of imaging operation where the imaging range of a camera is moved in the horizontal direction where at each imaging operation, portions of an object are included in the imaging range in performing preceding or succeeding imaging operation.
For example, as shown by FIG. 4, cameras 301 and 302 capable of imaging an object included in imaging ranges 307 and 308 each having a predetermined size by one imaging operation, are arranged such that the imaging ranges 307 and 308 overlap, to image objects 309 and 310. In this case, optical axes 303 and 304 of lenses 301a and 302a of the cameras intersect with each other by making an angle 305. In FIG. 4, a portion 311 where the imaging ranges 307 and 308 overlap is indicated by attaching hatched lines. The objects 309 and 310 are disposed in the portion 311. Distances (hereinafter, referred to as depth) from the camera 301 to the objects 309 and 310 differ from the depths from the camera 302 to the objects 309 and 310, respectively. Overlapped states of the objects 309 and 310 differ in view from the cameras 301 and 302 and therefore, a portion 321 of the object 310 is not seen from the camera 301 and seen from the camera 302.
FIGS. 5A and 5B show picture images 313 and 314 obtained by the cameras 301 and 302 through the imaging operation. The picture image 313 includes object images 317 and 318 representing the objects 309 and 310. The picture image 314 includes object images 319 and 320 of the objects 309 and 310.
Alternately, only one camera may be arranged in the same manner as in the camera 301 of FIG. 4. First the objects 309 and 310 are imaged by the camera, and then the camera is moved from the position where the optical axis of the lens coincides with the optical axis 303, to the position where the optical axis of the lens coincides with the optical axis 304, to image the objects 309 and 310 at the latter position. In this case, the positional relationship between the camera and the objects 309 and 310 in the first imaging operation equal to that between the camera 301 and the objects 309 and 310, and the positional relationship between the camera and the objects 309 and 310 in the second imaging operation is equal to that between the camera 302 and the objects 309 and 310. Consequently two picture images obtained in this case are equal to two picture images obtained by the cameras 301 and 302.
In carrying out pan-imaging by hand holding or imaging by a plurality of cameras, positions of the lenses 301a and 302a of the cameras 301 and 302 are shifted as shown by FIG. 4. Further, in many of combinations of camera and tripod, the rotational center of a camera does not coincide with the lens center of the camera and accordingly, more or less movement of the position of lens is caused even in the case where pan-imaging is carried out by using a tripod. These differences in the position of lens give rise to a parallax caused by a difference in depths of objects in the picture image.
For example, as shown by FIGS. 5A and 5B, although the portion 321 is imaged in the image 320 of the object 310 in the picture image 314, the portion 321 is not imaged in the image 318 of the object 310 in the picture image 313. Therefore, according to the picture images 313 and 314, respective shapes and overlapped states of the images 317, 318; 319, 320 of the objects 309 and 310 in the overlapped portion 311 of the imaging ranges 307 and 308 do not coincide with each other.
Accordingly, when a panoramic picture image 323 shown by FIG. 5C is formed by jointing the picture images 313 and 314 such that the positions of the picture images 313 and 314 are made to coincide with each other in order to make the images 317 and 319 of the object 309 coincide with each other, the images 318 and 320 of the object 310 do not coincide with each other but are shifted from each other. Conversely, when a panoramic picture image 324 shown by FIG. 5D is formed by jointing the picture images 313 and 314 such that the positions of the picture images 313 and 314 are made to coincide with each other in order to make the images 318 and 320 of the object 310 coincide with each other, the images 317 and 319 of the object 309 do not coincide with each other but are shifted from each other. Further, when a moving body is an object, in the case where respective imaging operations are shifted over time, with the movement of the body the position and the shape of the image of the object are changed in the respective picture images and therefore, the images of the object do not coincide with each other also in the case where a panoramic picture image is formed from these picture images as described above.
Further, according to the conventional picture image jointing technology, picture images are jointed by a joint line of a straight line or a straight line having a width. However, when there are differences among picture images as described above, picture images cannot often be composited adequately. Particularly, even when portions of picture images are naturally jointed, there causes shift or doubled imaging on joint lines in respect of portions resulting in parallax or including a moving body thereby causing significant deterioration in the quality of a panoramic picture image.